The major themes of this supplemental grant application to the Urolithiasis SCOR program relates to the further study of the pathophysiology of primary hyperparathyroidism in man and related animal studies concerned with the modes of action of 1,25(OH)2D3 and the parathyroid hormone. In particular the interrelated roles of parathyroid hormone and 1,25-dihydroxyvitamin D3 in determining the different clinical presentations of hyperparathyroidism will be studied. The clinical studies will also include the further evaluation of the role of enhanced oxalate absorption in the pathogenesis of renal calculi in patients with primary hyperparathyroidism. Studies in intact tissues and isolated membrane vesicles from transporting epithelia, i.e., intestine and renal tubule are planned in order to examine the cellular basis of intestinal oxalate transport, the cellular basis of calcium and phosphate transport and the mechanism by which the parathyroid hormone and 1,25(OH)2D3 control these processes. In addition, studies of the mode of intestinal oxalate absorption will be carried out in intact intestinal segments, and in isolated brush border membrane vesicles.